Fixes rescue doesn't honor enable password conf for v3

The rescue api should honor enable_instance_password conf
setting just like server creation and rebuild api does,
enables this flag will returning the instance password from
server API call rescue, If the hypervisor does not support
password injection then the password returned will not be
correct, this patch just fixes v3 rescue api, since change
return value of v2 could potentially break apps which depend
on this being returned.

DocImpact
Closes-bug #1213866

Change-Id: Ie8422979940bbde8c5749fcd3d6c735e88f78c6a
Merge "Fixes rescue doesn't honor enable password conf for v3"